Optical combiner energy harvesting

ABSTRACT

Powering an active/splitter and providing information to ONUs to cause adjustments to ONU operating wavelengths. An ONU may identify the port of a splitter to which the ONU is connected in order to make wavelength adjustments. Various techniques enable the ONU to identify from which port the ONU is receiving signals, such as a splitter that splits signals to ONUs in a cable network and signals to one or more ONUs the port to which it is connected. The splitter may lack electrical power and may perform the signal function by harvesting optical power from optical power provided to the splitter. In this manner, an active splitter may behave passively with respect to powering components in the absence of electrical power.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e)to U.S. Provisional Application No. 61/982,089, filed on Apr. 21, 2014;U.S. Provisional Application No. 62/043,787, filed on Aug. 29, 2014; andU.S. Provisional Application No. 62/043,793, filed on Aug. 29, 2014, theentire disclosures of each incorporated herein by reference.

Also, this application is related to U.S. application Ser. No.14/625,187 entitled “Active Optical Combiner for CATV Network” filedFeb. 18, 2015, the entire disclosures of each incorporated herein byreference.

BACKGROUND

Although cable television (CATV) networks originally delivered contentto subscribers over large distances using an exclusively radio frequency(RF) transmission system, modern CATV transmission systems have replacedmuch of the RF transmission path with a more effective optical network,creating a hybrid transmission system where cable content originates andterminates as RF signals over coaxial cables, but is converted tooptical signals for transmission over the bulk of the interveningdistance between the content provider and the subscriber. Specifically,CATV networks include a head end at the content provider for receivingRF signals representing many channels of content. The head end receivesthe respective RF content signals, multiplexes them using an RFcombining network, converts the combined RF signal to an optical signal(typically by using the RF signal to modulate a laser) and outputs theoptical signal to a fiber-optic network that communicates the signal toone or more nodes, each proximate a group of subscribers. The node thenreverses the conversion process by de-multiplexing the received opticalsignal and converting it back to an RF signal so that it can be receivedby viewers.

Cable television (CATV) networks have continuously evolved since firstbeing deployed as relatively simple systems that delivered videochannels one-way from a content provider. Early systems includedtransmitters that assigned a number of CATV channels to separatefrequency bands, each of approximately 6 MHz. Subsequent advancementspermitted limited return communication from the subscribers back to thecontent provider either through a dedicated, small low-frequency signalpropagated onto the coaxial network. Modern CATV networks, however,provide for not only a much greater number of channels of content, butalso provide data services (such as Internet access) that require muchgreater bandwidth to be assigned for both forward and return paths. Inthe specification, the drawings, and the claims, the terms “forwardpath” and “downstream” may be interchangeably used to refer to a pathfrom a head end to a node, a node to an end-user, or a head end to anend user. Conversely, the terms “return path”, “reverse path” and“upstream” may be interchangeably used to refer to a path from an enduser to a node, a node to a head end, or an end user to a head end.

Recent improvements in CATV architectures that provide furtherimprovements in delivery of content include Fiber-to-the Premises (FTTP)architectures that replace the coaxial network between a node and asubscriber's home with a fiber-optic network. Such architectures arealso called Radio Frequency over Glass (RFoG) architectures. A keybenefit of RFoG is that it provides for faster connection speeds andmore bandwidth than current coaxial transmission paths are capable ofdelivering. For example, a single copper pair conductor can carry sixphone calls, while a single fiber pair can carry more than 2.5 millionphone calls simultaneously. FTTP also allows consumers to bundle theircommunications services to receive telephone, video, audio, television,any other digital data products or services simultaneously.

One existing impairment of RFoG communication channels is Optical BeatInterference (OBI), which afflicts traditional RFoG networks. OBI occurswhen two or more reverse path transmitters are powered on, and are veryclose in wavelength to each other. OBI limits upstream traffic, but alsocan limit downstream traffic. Existing efforts at mitigating OBI havefocused on Optical Network Units (ONUs) at the customer premises, or onthe CMTS at the head end. For example, some attempts to mitigate OBImake the ONUs wavelength specific while other attempts create anRFoG-aware scheduler in the cable modem termination system (CMTS). Stillothers attempts have included changing ONU wavelengths on the fly. Dueto the fundamental nature of lasers and Data Over Cable ServiceInterface Specification (DOCSIS) traffic, none of the above techniquesyield satisfactory results as wavelength collisions still occur or costis high.

Thus, it may be desirable in RFoG deployments to further reduce oreliminate OBI.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating embodiments described below, there areshown in the drawings example constructions of the embodiments; however,the embodiments are not limited to the specific methods andinstrumentalities disclosed. In the drawings:

FIG. 1 depicts a radio frequency over glass (RFoG) architecture.

FIG. 2 shows an RFoG architecture improved in accordance with thedisclosed techniques.

FIG. 3A illustrates an embodiment for an optical network unit (ONU)configured to listen to a forward wavelength signal passed through awave division multiplexer. FIG. 3B illustrates another embodiment for anoptical network unit (ONU) configured to listen to a forward wavelengthsignal passed through a wave division multiplexer.

FIG. 4 depicts an embodiment for a 1×N passive splitter with reflection.

FIG. 5 depicts an embodiment for an active splitter with powerharvesting techniques for signaling.

FIG. 6 depicts another embodiment for an active splitter with powerharvesting techniques for signaling.

FIG. 7 depicts an embodiment for an active splitter with piezosignaling.

FIG. 8 depicts an embodiment for an active and passive splitter system.It is noted that while the accompanying Figures serve to illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments, the conceptsdisplayed are not necessary to understand the embodiments of the presentinvention, as the details depicted in the Figures would be readilyapparent to those of ordinary skill in the art having the benefit of thedescription herein.

DETAILED DESCRIPTION

Configuring optical network unit (ONU)s to receive signals at differentwavelengths may facilitate the prevention or elimination of OBI.Disclosed herein are techniques for adjusting a wavelength at an ONU byproviding information to the ONU to perform the adjustment. Thedisclosed techniques may include the ONU identifying the port of asplitter to which the ONU is connected in order to make wavelengthadjustments. Various techniques are described herein to enable the ONUto identify from which port the ONU is receiving signals. For example,as described in more detail below, a splitter that splits signals toONUs in a cable network may signal to one or more ONUs the port to whichit is connected. The splitter may perform the signal function byharvesting optical power from optical power provided to the splitter. Inthis manner, an active splitter may behave passively or in a passivemode with respect to the receipt of power, not requiring remote power,such as remote electrical or remote optical power, to perform thesignaling to the ONU. Thus, a splitter lacking electrical power may beable to harvest power for signaling information to the ONU for OBIprevention, functioning as an optical combiner with energy harvesting.The amount of power scavenged may be a small fraction of availableoptical power present within the combiner to transmit signals. In theabsence of any remote optical powering or any specific provision ofoptical power to power the splitter, the scavenged portion of existingoptical signal power input is made useful by the disclosed techniques.

Modern cable television (CATV) transmission systems have replaced muchof the legacy radio frequency (RF) transmission path with a moreeffective optical network, creating a hybrid transmission system wherecable content originates and terminates as RF signals over coaxialcables, but is converted to optical signals for transmission over thebulk of the intervening distance between the content provider and thesubscriber. Specifically, CATV networks include a head end at thecontent provider for receiving RF signals representing many channels ofcontent. The head end may receive the respective RF content signals,multiplex the signals using an RF combining network, convert thecombined RF signal to an optical signal (e.g., by using the RF signal tomodulate a laser) and output the optical signal to a fiber-optic networkthat communicates the signal to one or more nodes, each proximate to agroup of subscribers. The node may then reverse the conversion processby de-multiplexing the received optical signal and converting it back toan RF signal so that it can be received by viewers.

Improvements to CATV architectures that provide further improvements indelivery of content include Fiber-to-the Premises (FTTP) architecturesthat replace the coaxial network between a node and a subscriber's homewith a fiber-optic network. Such architectures are also called RadioFrequency over Glass (RFoG) architectures. A benefit of RFoG is that itprovides for faster connection speeds and more bandwidth than currentcoaxial transmission paths are capable of delivering. For example, asingle copper pair conductor can carry six phone calls, while a singlefiber pair can carry more than 2.5 million phone calls simultaneously.FTTP also allows consumers to bundle their communications services toreceive telephone, video, audio, television, any other digital dataproducts or services simultaneously.

In telecommunications, radio frequency over glass (RFoG) is a deep-fibernetwork design in which the coax portion of the hybrid fiber coax (HFC)network is replaced by a single-fiber passive optical network (PON). TheSociety of Cable and Telecommunications Engineers (SCTE) has approvedstandards for implementing RFoG, also approved by the American NationalStandard Institute (ANSI).

An RFoG topology may include an all-fiber service from the headend to afield node or optical network unit (ONU), which is typically located ator near the user's premises. In a cable network headend, a downstreamlaser may send a broadcast signal that is optically split multipletimes. The optical network unit, or ONU, recovers the RF broadcastsignal and passes it into the subscriber's coax network. Downstream andreturn-path transmission use different wavelengths to share the samefiber (typically 1,550 nm downstream, and 1,310 nm or 1,590/1,610 nmupstream). The return-path wavelength standard is expected to be 1,610nm, but early deployments have used 1,590 nm. Using 1,590/1,610 nm forthe return path allows the fiber infrastructure to support both RFoG anda standards-based PON simultaneously, operating with 1,490 nm downstreamand 1,310 nm return-path wavelengths. Both RFoG and HFC systems canconcurrently operate out of the same headend/hub, making RFoG a goodsolution for node-splitting and capacity increases on an existingnetwork.

RFoG allows service providers to continue to leverage traditional HFCequipment and back-office applications with the new FTTP deployments.For example, cable operators can continue to rely on the existingprovision and billing systems, Cable modem termination system (CMTS)platforms, headend equipment, set-top boxes, conditional accesstechnology and cable modems while gaining benefits inherent with RFoGand FTTx.

FIG. 1 shows an exemplary RFoG system 10, where a head end 12 deliverscontent to an ONU 14 at a customer's premises through a node 16. An RFoGtopology includes an all-fiber service from the headend 12 to a fieldnode or optical network unit (ONU), which is typically located at ornear the user's premises. In the headend 12, a downstream laser sends abroadcast signal that is optically split multiple times. The opticalnetwork unit 14, or ONU, recovers the RF broadcast signal and passes itinto the subscriber's network, which may be coaxial or also upgradedwith fiber communication.

The head end 12 may include a transmitter 18 that delivers a downstreamsignal to one or more 1×32 passive splitters 20 that includes 32 outputports, each output port connected to a wavelength division multiplexer(WDM) splitter 28 that delivers the downstream content over a fibertransmission segment 24 to the node 16. The node 16 may include another1×32 splitter 22, where each output port of the splitter 22 is connectedvia another fiber segment 26 to a particular ONU 14 at a subscriber'spremises.

Optical networking units (ONUs) in an RFoG environment may terminate thefiber connection at a subscriber-side interface and convert traffic fordelivery over the in-home network at the customer premises. Coaxialcable can be used to connect the ONUs of an RFoG network to one or moreuser device, wherein the RFoG user devices can include cable modems,EMTAs, or set-top boxes, as with the user devices of an HFC network. Forexample, an R-ONU may connect to set-top boxes, cable modems, or likenetwork elements via coaxial cable, and one or more of the cable modemsmay connect to the subscriber's internal telephone wiring and/or topersonal computers or like devices via Ethernet or Wi-Fi connections.

Those of ordinary skill in the art will appreciate that the foregoingarchitecture is illustrative only. For example, the number of ports ofthe splitters 20 and 22 may be changed, as desired. It should also beunderstood that the head end 12 may include more splitters 20, eachsplitter having outputs connected to a respective node so as to serve agreat number of subscribers.

Along the return path from the subscriber's ONU 14 to the head end, thesplitter 22 operates as a combiner, i.e. for a 1×32 portsplitter/combiner 22, up to 32 ONUs may deliver return path signals tothe node 16, which combines them for upstream transmission along fiberlength 24. Each of the signals from the respective fiber links 24 isthen separated from other signals by the WDM 28 to be received by aseparate receiver 30 in the head end 12. The signals from the respectivereceivers are then combined by a combiner 32 for transmission to a CableModem Termination Service (CMTS) in the head end 12. The signals arecombined in the RF domain in the headend 12 by the combiner 32, beforebeing connected to the CMTS upstream port. Combined with the forwardpower limit on the fiber, the combined signals may require one forwardfiber 24 (L1 km) per group of 32 subscribers.

In the forward direction, the forward transmitter is provided to ahigher power multi-port amplifier that distributes power. For example,in the head end 12, the transmitter 18 provides output to an ErbiumDoped Fiber Amplifier (EDFA) 34 that internally distributes power overthe 32 outputs of the combiner 20, each output operated at a relativelyhigh power, e.g. approximately 18 decibel-milliwatts (dBm). The WDM 28may transmit 1550 nm light from the EDFA 34 in the forward direction anddirect reverse light, typically at 1610 nm or perhaps 1310 nm in thereverse direction to the receivers 30. The WDM 28 may be connected to afiber of length L1 that feeds the splitter 22 in the node 16.

The outputs of the splitter 22 may each be provided to second fibers oflength L2 that are respectively connected to ONUs 14 at the subscriberhomes. In embodiments, L1+L2 may be up to 25 km. The ONUs 14 convert theforward transmitted light to RF signals for the in-home coaxial network.In the return direction, the ONUs 14 may also receive RF signals fromthe in-home network and modulate these signals onto a laser, operatingat 1610 nm for example, and the laser's output is sent upstream into thefiber L2. The upstream signal may be combined with other upstreamsignals in the combiner 22 and transmitted further upstream in the fiberL1. At the WDM 28 the upstream signals are directed towards the head endreceivers 30.

The loss budget for 32 subscribers and 25 km of fiber requires onereceiver in the head end 12 for every group of 32 subscribers; given anupstream transmission power of 3 dBm, the receivers 30 and the WDM 28may typically operate at a power between −18 and −21 dBm, making a goodsignal to noise ratio challenging, such that band limited receivers areusually required for acceptable performance. Furthermore, the opticalcombiner 22 may be passive and combine multiple optical inputs to asingle output. Thus, by definition the optical combiner 22 will createOBI between these inputs, as described earlier and will therefore createnoise in the RF domain at the head end receivers 30. Furthermore, assumea loss of around 24 dB in the forward path; for an EDFA output power of18 dBm per port this provides −6 dBm power to the receivers. This issufficient for acceptable performance at the ONU to 1 GHz, provided lownoise high gain receivers are used.

From a splitter that distributes light to subscribers and combinesreturn light from the subscribers at a penalty, there can be a long link(e.g., up to 25 km with an additional 6 dB of loss) back to a headend orhub where the combined return sources are detected at a receiver. Thetotal loss is high such that the receiver SNR is degraded. Furthermore,typically up to 8 receiver outputs are combined onto on CMTS return portthat thus handles around 256 subscribers. In this combining, thereceiver thermal noise adds up and unless means are implemented on thereceivers to turn them off in the absence of signal the SNR is degradedby a further 9 dB. With such means the SNR is still degraded by up to 6dB when up to 4 return transmitters are on simultaneously, a validoperation mode of the return network.

The phenomenon of optical beat interference (OBI) may occur in RFoGsystems when two return transmitters hit a receiver simultaneously onthe same wavelength. In a cable system, for example, this condition thatmay cause OBI can easily occur in multiple-dwelling unit (MDU)applications of DOCSIS-based systems with bonded upstream channels.Optical Beat Interference (OBI) is a signal degradation that occurs whentwo or more lasers with closely-spaced optical frequencies transmitsimultaneously from two ONUs.

The disclosed techniques for eliminating OBI are desirable, and thedisclosed manner for eliminating OBI may enable higher capacity in theupstream and downstream. Further, the disclosed splitter/combiner andfeatures of the combiner may enable RFoG coexistence alongsidetraditional HFC/D3.1 systems and future potential PON systems. Theelimination of OBI is critical in some systems to unlock the vastpotential of the optical fiber. Described in more detail herein areembodiments for an architecture that incorporates the disclosed opticalcombiner system with a self-configuring ONU.

FIG. 2 shows an improved system 100 for delivering content, e.g., CATVcontent, to a plurality of subscribers over a network, such as the RFoGnetwork described above. The architecture includes a head end 110 havinga transmitter 112 and receiver 114, each connected to a WDM splitter 116that outputs a signal to, and receives a signal from, a fiber link 118of L1 km. The fiber link 118 is connected to an active splitter/combinerunit 120. The splitter/combiner unit 120 may include a WDM 122 that mayseparate forward path signals from reverse path signals. The forwardpath signal from the WDM 122 is provided to an EDFA 124 that outputs anamplified optical signal to an active 1×32 splitter 126 that has 32output ports communicable to respective second fiber links 128. At eachport, the power level is modest, in the 0-10 dBm range.

In the reverse direction, the 1×32 port splitter 126 operates as anactive combiner 126, and includes a WDM per port directing upstreamlight to a detector that converts the received optical signal to anelectrical signal and amplifies it in the RF domain and provides theelectrical signal to a transmitter 129 that outputs light at, forexample, 1610 nm, 1310 nm, or some other appropriate wavelength,provided to the WDM 122, which in turn directs the upstream light intofiber 118. At the head end, the fiber 118 is connected to WDM 116 thatdirects the upstream light to the receiver 114.

Each of the 32 ports of the splitter/combiner 126 output, through arespective fiber 128, outputs a respective signal to a second activesplitter/combiner unit 130, which may be of the same type andconfiguration as the splitter/combiner unit 120. The length(s) of thefiber 128 may vary with respect to each other. The output power persplitter port is low, around 0 dBm. The splitter ports are connected toONUs 140, for instance in a Multiple Dwelling Unit (MDU) or aneighborhood, via fiber 132 of length L3. In a basic RFoG system, thesum of the fiber lengths L1+L2+L3 is up to 25 km. The system 100,however, will permit a higher total length of fiber between the head endand the ONUs, such as 40 km, because the system 100 can tolerate ahigher SNR loss, as further described below.

The upstream signals from the ONU 140 may be individually terminateddirectly at the active splitter/combiner unit 130. Even for ONUsoperating at 0 dBm, the power reaching the detectors is around −2 dBm(the fiber 132 is a short fiber up to a few km, and the WDM loss insidethe active combiner is small). This is almost 20 dB higher than inexisting RFoG systems, meaning that the RF levels after the detector inthe splitter 134 are almost 40 dB higher than in existing RFoG systems.As a consequence, the receiver noise figure is not critical and highbandwidth receivers can be used with relatively poor noise performance.The received RF signal is re-transmitted via the transmitter 136 alongthe reverse path into fiber 128 and received and retransmitted by thepreceding active splitter/combiner unit 120 and thereafter to the headend 110. Although the repeated re-transmission may lead to someincremental reduction in SNR, improvements in SNR from the activearchitecture provide much greater overall performance relative totraditional RFoG systems. More importantly, because all reverse signalsmay be individually terminated at separate detectors, such as a multipledetector receivers in a transmission line detector structure withincombiner/splitter units 126 and 134 and the signals re-transmitted atupstream lasers transmitters 129 and 136, there can be no optical beatinterference (OBI) between different reverse signals. The reversesignals are not combined optically, i.e., the reverse signals areindividually detected and electrically summed in detector transmissionline structures in 126/134, hence OBI cannot occur.

In the forward direction there may be multiple EDFAs, e.g., 124, 135;these EDFAs are cost effective single stage devices with low powerdissipation—typically 2 Watts or less. Cascading the EDFAs result in anaccumulation of noise due to the finite noise figures of the EDFAs.Whereas the active splitter architecture does not require the EDFAs (thehigh power head end 110 EDFA (not shown) could still be used to providepower to the ONUs 140) the use of EDFAs 124, 135 inside the activesplitter units provides some advantages. For example, the complexity andpower dissipation of equipment in the head end 110 is greatly reduced,as is the fiber count emanating from the head end 110. The amount ofpower delivered to the ONUs 140 is readily increased from a typical −6dBm to approximately 0 dBm. As a consequence, ONU receivers obtain 12 dBmore RF level from their detectors and do not need as high an SNR orgain. Even with relaxed SNR requirements at the ONU receivers, the SNRimpact due to EDFA noise is easily overcome due to the higher receivedpower. In addition, more spectrum can be supported in the forwarddirection with an acceptable SNR relative to current architectures, suchas 4 GHz instead of 1 GHz in current RFoG. Hence total data throughputrates can grow significantly without a change in operation to permit forexample, services that provide 40 Gbps download speeds and 10 Gbpsupload speeds.

As described herein, eliminating OBI is desirable. In order to preventOBI, ONUs may be set at different wavelengths. However ONUs are unawareof or do not know the wavelength of other ONUs, and also do not knowwhat port of a passive they are connected to hence the wavelength to setthe ONU to is not known. Further, there is a demand for splitting asignal, which typically requires 2 or 3 watts of power for a photonharvester to handle. Thus, the appeal of using an active combiner islimited because, for example, for an active combiner to function, 2+watts of power are needed.

In some embodiments, the optical combiner such as those shown in FIGS. 1and 2 provides upstream and downstream RFoG capability and a completelytransparent and reciprocal avenue for PON transmission. The opticalcombiner may enable complete transparency for PON deployments. Forexample, the optical combiner may enable OBI free and high capacityfeatures by deployment in compatible HFC D3.1 capable FTTH networks.Likewise, the optical combiner may be incorporated in to GPON, 1G-EPON,XGPON1, 10G/1G-EPON, 10G/10G-EPON. The compatibility with HFC and D3.1enables the disclosed optical combiner to be deployed alongside acurrent HFC network, and is D3.1 ready. The optical combiner may bedeployed on a fiber node, on multiple dwelling unit (MDU) and on singlefamily home (SFU) deployments.

Embodiments for an RFoG combiner include preventing or eliminating OBIat the combiner as opposed to managing it at the extremities of thenetwork (such as using a CMTS scheduler at the headend side of thenetwork or wavelength specific ONUs at the subscriber end of thenetwork). Embodiments are described that enable elimination of OBI. Thedisclosed optical combiner may be used to eliminate OBI, enhancecapacity, and/or enable multiple services in RFoG, the cable version ofFTTH networks.

The disclosed optical combiner may be independent of ONUs, Cable Modemsand CMTSs. The disclosed optical combiner may be CMTS agnostic, thusrelieving the burden of creating an RFoG aware scheduler that is bothrestrictive and time consuming. The optical combiner assists to make acable version of FTTH more feasible, as compared to the PONalternatives. For example, in embodiments, the disclosed opticalcombiner has a reciprocal PON Pass thru capability of the opticalcombiner along with a high upstream and downstream capacity, whichassists RFoG deployment without interruption to the underlaid system orimpairment to future inclusion of PON functionality, such as later PONdeployment on an RFOG system.

In some embodiments, the optical combiner has 32 ports, but onlyrequires one transmit port, one receive port, and one WDM component atthe headend. Thus, instead of requiring 32 WDMs and 32 receive ports,the disclosed optical combiner may save on head end space and power. Thecombiner may be an active device that needs approximately 2 Watts ofpower. The optical combiner may be powered by power sources readilyavailable in the RFoG system, or power can be provisioned in to theoptical combiner. The power source may include a battery back-up orsolar/fiber power alternatives. If the power is lost and the battery hasalso drained, the entire reciprocal PON transmission is unaffected. Theupstream RFoG transmission is however stopped. In a conventional RFoGsystem it would have been stopped also because the preponderance of OBIwould have severely impaired the system anyway if the system was atraditional RFoG system with a passive combiner. Also in case of a powerloss ONU (Optical Networking Unit) at the homes would cease to functionsuch that without any power backup such systems will cease to function,whether those are RFoG or PON systems, with or without the activecombiner disclosed here. The headend optical receiver may only need aninput power range from 0 . . . −3 dBm, and require 15 dB less RF outputpower due to the absence of the RF combiner such that with such a highoptical input power and low RF output power requirement the gain can below.

The disclosed optical combiner may preferably eliminate OBI, making anOBI-free system. The optical combiner enables long reach and largesplits, e.g., Up to 40 km and 1024 Splits, which will expand evenfurther. The high upstream and downstream capacity enabled by thedisclosed optical combiner includes up to 10G DS/1G US, and as high as40G DS/10G US.

In embodiments, the disclosed optical combiner prevents interference inRFOG deployments in the combiner rather than preventing interferenceusing measures taken in the ONU where previous attempts have failed orproven to be cost-prohibitive.

Traditional RFoG architectures have a fixed power budget. This meansthat as fiber length between the head end and the ONUs increases, asmaller number of splits may be used. Conversely, the more splits thatare desired, the less fiber length may be deployed. The disclosed activearchitecture, however, enables fiber length of up to approximately 40 kmirrespective of the number of splits used, meaning that the disclosedactive architecture permits fiber lengths of 40 km or more along with alarge number of splits, e.g. 1024, thereby advancing FTTP topology anddeployment.

The overall cost of the active splitter architecture shown in FIG. 2 issimilar to that of a traditional RFoG solution. The cost of activesplitter EDFA gain blocks and WDM and detector components in the activearchitecture is offset by the elimination of head end gear such asreceivers, high power EDFAs and combiners. A cost reduction of the ONUsthat can operate with lower output power further supports the activesplitter architecture. Further advantages of the active splitterarchitecture may include a reduction in outgoing fiber count from thehead end, which can have a large impact on system cost, as well as anoption to use 1310 nm reverse ONUs while staying within a typical SNRloss budget, which can further reduce costs. Also, the system shown inFIG. 2 exhibits increased bandwidth relative to what existing RFOGarchitectures are capable of providing, avoiding limits on service groupsizes and concomitant requirements for more CMTS return ports. Finally,unlike OBI mitigation techniques in existing RFoG architectures, thesystem shown in FIG. 2 does not require cooled or temperature controlledoptics and bi-directional communication links that necessitateadditional ONU intelligence.

Each of these factors provides a further cost advantage of an activesplitter solution over existing RFoG architectures. Required space andpower in the head end is also reduced; the active splitter solutionrequires one transmit port, one receive port and one WDM component.Existing RFoG architectures, on the other hand, requires transmit ports,multi-port high power EDFAs, 32 WDM's, 32 receiver ports, and a 32-portRF combiner. Existing RFoG architectures require very low noise, highgain, and output power receivers with squelch methods implemented toovercome power loss and noise addition in the RF combiner. The system100 shown in FIG. 2, conversely, works with input power normally in the0-3 dBm range, little gain is required, and requires 15 dB less poweroutput due to the absence of the RF combiner before the CMTS.

The disclosed optical combiner unit may be independent of ONUs CableModems and CMTSs. The disclosed optical combiner may be CMTS agnostic,thus relieving the burden of creating an RFoG aware scheduler that isboth restrictive and time consuming. The optical combiner assists tomake a cable version of FTTH more feasible, as compared to the PassiveOptical Network (PON) alternatives. For example, the disclosed opticalcombiner unit may have a reciprocal PON pass-thru capability of theoptical combiner unit along with a high upstream and downstreamcapacity, which assists RFoG deployment without interruption to theunderlying system or later PON deployment on an RFoG system.

Preferably, the disclosed optical combiner unit implements atransmission line approach to combine multiple optical photodetectors ina single optical receiver. This may be accomplished in unidirectional orbidirectional configurations. A unidirectional system provides nocontrol communication signals from an active optical splitter to an ONU,i.e. control communication signals only pass from an ONU to an activesplitter. Thus, in a unidirectional system, an active optical splittersimply accepts an output level from an ONU and operates with that outputlevel. A bidirectional system passes control signals from an activeoptical splitter to ONUs instructing them to adjust their output power;this type of system permits accurate equalization of the input levels tothe active optical splitter from each ONU.

Some active splitter/combiner systems may preferably include redundancywhere active optical splitters switch their return laser power (thereturn laser that carries the combined information of the ONUs connectedto it) between a high and a low power state or operates this laser in CWmode. In that case an upstream head end or active optical splitter caneasily detect loss of power at an input port and enable a second inputport connected to another fiber route to receive the information, in theforward path the other fiber route would also be activated in this casebecause generally the forward and reverse light share the same fiber.Also, some active splitter/combiner systems may include a reverse laserin the active optical splitter that adjusts its power output as afunction of the number of ONUs transmitter to the active opticalsplitter and the photocurrent received from these ONUs. Still otheractive splitter/combiner systems may have a gain factor and reverselaser power of the active optical splitter set to a fixed value.

Preferably, the disclosed optical combiner unit is able to configureitself under changing circumstances. Instances occur in which cablemodems in the ONU are required to communicate with the CMTS even ifthere is no data to be transmitted. Usually, however, the ONU is turnedoff during periods when there is no data to be transmitted between theONU and CMTS, and a cable modem could go hours before receiving orsending data. Thus, in some embodiments the disclosed combiner unit maybe configured to stay in communication with the CMTS. Cable modems maybe required to communicate back to the CMTS once every 30 seconds, orsome other appropriate interval.

Disclosed herein are techniques for eliminating power requirements in acombiner but still preventing or eliminating OBI. In other words, therequirement for power may be eliminated, though providing power is stillallowed. In embodiments, a photon harvester in an optical combiner hasactive downstream signaling. In embodiments, the photon harvesterprovides energy powering a mechanism in the passive combiner that canmodulate a downstream light or add a modulated light source to thedownstream light being split by the passive combiner. In embodiments,the optical combiner functions as a passive combiner with energyharvesting, and is located between an active splitter 130 and an ONU140, receiving downstream light from the active splitter and upstreamlight from one or more ONUs connected to one or more ports of thepassive splitter. Note that such a passive splitter does contain activeelectronics, however it does not require electrical powering so for allintents and purposes it functions as a ‘passive splitter’ except that ithas added signaling capabilities.

As downstream light enters the combiner, a portion of the light isdetected by a photodiode and the charge produced in the photodiode isingested by a capacitor. The capacitor holds its charge, and oncecompletely charged, can discharge the charge on to a PZT driver circuitor to an LED driver circuit, to create modulated light to travel acrossthe active downstream channel. The ONU recognizes the signal and, inresponse to the signal, can change its wavelength. For example, if thedownstream signal output from the photon harvester identifies port 1 asa port that should be operated at wavelength x, the ONU can tune towavelength x in response to the downstream signal. Thus, the combinercan inform the ONU to which port it is connected.

In response to the downstream signal received by the passive combiner,the ONU can use the information to connect itself directly to a properport of the combiner and configure itself for the port. The disclosedtechniques provide the option to have a single unit, non-active, andcompletely OBI eliminating passive combiner. Non-active meaning that thesplitter does not require electrical power to operate such that to theuser it appears as a ‘non-active’ or ‘passive’ splitter. It can containactive electrical components and it obtains power to operate fromharvesting photons of a fraction of downstream light directed at aphotodiode. In implementations, embodiments for the disclosed activesplitters may be located temporally at an extremity of the network whereno power is available. The combination of active splitters and passivesplitters with downstream signaling together can provide more enhancedcoverage to create an OBI free portion of the network. A passivesplitter signals to the ONU what port it is on, the splitter performsthe signal function by harvesting optical power from optical powerprovided to the splitter such that the splitter does not requireelectrical power and in that sense remains a ‘passive’ device.

As described in more detail, below, a priori knowledge of the combinerfor ONU configuration for communication with the combiner is notnecessary, as the ONU is able to employ the disclosed techniques todetermine its configuration in a uni-directional manner. The combinerdoes not require electrical power to communicate its settings to theONU, and the photon harvester can be used for low speed signaling.

The ONU can configure itself based on various content in the downstreamsignal. For example, in embodiments, an ONU with a tone input includesan ONU that can listen for tones or frequency-shift keying (FSK) signalsto determine at what wavelength it should operate. The ONU can receiveinstructions via the downstream signal to reduce chatter. The ONU candecode signaling informing about the port of an active 1×N splitter towhich it is connected. Active/passive splitters for RFoG may includeautomatic ONU wavelength assignment for NOBI (No OBI) and automaticsystem mapping. An ONU may signal its current wavelength andidentification code for instance by using a FSK (Frequency Shift Keying)to an upstream passive splitter or active splitter. Whereas the passivesplitter may simply pass the signal upstream, an active splitter mayinterpret the signal. Since the active splitter can detect at what portthe signal was received it can map the identification code of ONUs toits ports. In case a passive splitter with power harvesting thatinstructs the ONU to pick a particular wavelength depending on thepassive splitter port was involved then the wavelength chosen is anindication of the port number of the passive splitter that the ONU wasconnected to. Thus the system can be automatically mapped.

In embodiments, the ONU has a tone output. The ONU can label its outputsignal with a tone or FSK signal representing its current wavelength.The ONU can also listen for tones or FSK signals to discover at whatwavelength other ONUs are operating. In embodiments, the ONU can adjustits wavelength to avoid wavelengths taken by other ONUs. In embodiments,the ONU can follow a statistical scheme wherein it reacts only to afraction of signals indicating a wavelength conflict. In embodiments thepassive splitter may reflect a fraction of upstream signaling back toONUs such that ONUs can receive wavelength labels from other ONUsconnected to that passive splitter. Wavelength labels may be, forinstance, tone signals encoding information such as a wavelength atwhich another ONU is operating.

The ONU may be configured to generate or identify OBI detect signals.For example, the ONU can keep track of its own activity to determine ifit could cause an OBI event, and/or the ONU can listen for tones or FSKsignals to discover if an OBI event has taken place. Such signals may begenerated by an active splitter configured to detect OBI events andsignal detection of such events downstream to ONUs. The ONU can adjustits wavelength if an OBI event has been signaled that it could havecaused. The ONU can follow a statistical scheme wherein it reacts onlyto a fraction of such events.

In embodiments, the ONU is connected to an active splitter with FSKtransmission capability. The ONU can keep track of its own activity todetermine if it is part of a current event. For example, the ONU canlisten for tones or FSK signals to decode information sent downstream byan active upstream device in response to ONU activity. Such downstreaminformation may include a list of currently active upstream ports at theactive splitter. The ONU can discover the port of that upstream devicethat it is connected to by correlating to its own activity. The activesplitter may also signal wavelength label information that it hasreceived from ONUs at ports to downstream ONUs. The ONU can adjust itswavelength if a wavelength conflict is signaled with another ONU at thesame port, particularly when the ONU receives a wavelength labelidentical to its own label at the port that it is connected to when theONU itself was not active at that time. The ONU can follow a statisticalscheme wherein it reacts only to a fraction of such events

FIGS. 3A and 3B below depict embodiments of ONUs configured to listen toFSK.

FIG. 3A illustrates an ONU configured to listen to a forward wavelengthsignal 307 passed through the WDM device 310 to the detector 304 throughthe RF path amplifier 308 or picked up before the amplifier 308 (dashedsignal 305) for low frequencies. As described above, the ONU 140 can beconfigured to listen to other wavelengths through the leakage throughthe WDM component 310 to the detector 304 (can be as much as −15 dB).The ONU 140 may be configured to listen to reflection of wavelengths 309by the WDM device 310 to the laser 302 by using the laser 302 aphotodiode when the laser is off (dashed line). The reflection ofwavelengths by a WDM device 310 may be strongest in wavelengths selectedby the WDM device 310, and weaker for other wavelengths (−40 dB or moreattenuation). The laser 302 can be slightly reverse-biased to improveresponse when used as a photodiode. FIG. 3B illustrates the concepts inFIG. 3A, but with the WDM 310 used such that leakage of wavelengths tothe laser is larger (˜−15 dB). In FIG. 3A, WDM component 310 passeslight to the detector 304A, and in FIG. 3B the WDM 310 reflects light tothe detector 304B in FIG. 3B. Thus, the WDM component 310 reflects lightto and from the laser 302A in FIG. 3A and it passes light to and fromthe laser 302B in FIG. 3B.

FIG. 4 depicts an embodiment for a passive splitter with reflection. Forexample, FIG. 4 depicts a simple view of the combiner 120 or 130 fromFIG. 2 without all components, but for the purposes of illustrating thereflection by the 1×N splitter. In this figure, a 1×N splitter (1×4 inthis example) that transmits to ONUs, such as ONU 407 and 408, overrespective fibers, such as fiber 405 and 406, respectively, is precededby a coupler 404. The coupler 404 may couple a small fraction of reverselight 409 (e.g., 10% here) to a reflecting device 410 such that thereverse light is re-injected in the forward direction 411 into thecoupler 404. The light directed to the reflector at 409 a and the lightreflected by the reflector at 409 b is opposite in direction.

Thus, when an ONU served by the splitter, e.g. ONUs 407, 408, is active,a fraction of the ONU's light is reflected and distributed over theother ONUs. The other ONUs can then monitor the wavelength indicatingtone(s) produced by the active ONU(s) and move their own wavelengthsetting to prevent conflict. A downside is that the reflection must beweak or else noise is generated due to multiple reflections in the pathbetween ONU (as an imperfect connection may be assumed) and thereflector preceding the splitter. With a perfectly terminated ONU,re-reflection could be suppressed sufficiently and with sufficientisolation the reverse laser would not self-interfere with reflectedsignals. The reflector 410 may be made polarization dependent (pol) suchthat the reflection occurs at a polarization state orthogonal to theincoming polarization, for instance by applying similar means as inpolarization (in)dependent isolators. This can effectively suppressself-interference of a re-reflected signal.

FIG. 5 depicts an embodiment for an active splitter with signaling. Theimplementation in FIG. 5 does not require electrical power. A 1×Nsplitter 516 (1×4 here) is preceded by a tap 502 with input 520 andoutput 519 that couples a fraction of light 503 to a detector 504feeding a power harvesting circuit (<1 mW) 508. The power harvestingcircuit 508 includes detector 504 and power circuit 508. The powercircuit 508 can include capacitors and/or batteries. The LEDs 505, 506may be used to emit light (so they consume power). Thus, the powerharvesting circuit can collect power to operate LEDs 505, 506 at lowduty cycle each at their own rate, e.g., at 1550 nm. to inject forwardsignaling into the splitter to tag port information to the port outputs.The ONUs, e.g., ONUs 511 and 512 receiving signals from the splitterover respective fibers 513, 514, read this information and setwavelengths according to their assigned port. LEDa 505 is received bythe upper two output ports A,B of this 1×4 splitter 516 with an extrainputs for LEDa. This is accomplished by constructing the splitter 516using a 2×2 splitter 516 a and two 1×2 splitters 516 b and 516 c. LEDbis divided by splitter 517 c and coupled to fibers 513 and 514 andreceived by the middle two output ports B, C via 10% couplers 517 a and517 b after the splitter 517 c, the lower port D receives no LED output.For a 1×8 splitter 3 LEDs are needed; N LEDs are needed for a 1×2^Nsplitter. It should be noted that in upstream direction the splitter 516acts as a combiner to combine upstream signals sent from the ONUs to putthem out at input port 520.

FIG. 6 depicts another embodiment for an active splitter with signaling.The implementation illustrated in FIG. 6 does not require electricalpower. A 1×N splitter 602 (1×4 here) is preceded by a tap 604 thatcouples a fraction of light to a detector 608 feeding a power harvestingcircuit 610 (<1 mW). This collects power in a small capacitor for shortburst operation (e.g., 10-100 usec duration). The Rx/Tx 611 represents areceive signals resulting from light detected by the LED 612 andtransmit signals to the LED 612 that converts these signals to light.The LED 612 is used as a detector that will produce a voltage with atone/FSK signal when an ONU transmits in reverse direction with such atone or FSK signal. When sufficient power has been collected the LED 612is then turned on and answers with information in the forward band as atone/FSK signal that represents the information that had just beendetected on the LED 612. Re-charge time to recover from such atransmission is expected to be in the 1-10 msec range. A small ceramiccapacitor of around 10 uF is expected to be sufficient for energystorage. This embodiment is comparable to the passive reflector conceptshown in FIG. 4 without a risk for interference due to re-reflection andwithout a need for the ONU 614, 616 to detect signals that are not inthe forward band. The use of an LED 612 prevents OBI with the forwardsignal and saves power. The LED does not tell the ONU what port it ison, but it does tell other ONUs what wavelength an active ONU istransmitting at so that the other ONUs can move to another wavelength

FIG. 7 depicts an embodiment for an active splitter with piezosignaling. The implementation shown in FIG. 7 does not requireelectrical power. A 1×N splitter 708 (1×4 here) is preceded by a tap 702that couples a fraction of light 701 to a detector 704 feeding a powerharvesting circuit 706 (<1 mW). The power harvesting circuit 706collects power in a small capacitor for short burst operation (e.g.10-100 usec duration). During operation piezo actuators (PZT) 710, 712induce a vibration in a partial or full fiber bend loop (radius ˜10 mmorder of magnitude) in the output fibers 713, 715. The vibration causesa loss modulation of the forward light that is detected by the ONUs,e.g., ONUs 714, 716. The ONUs 714, 716 have a low frequency signalreceiver coupled to the detector in the ONU such as detector 304 inFIGS. 3A and 3B with and output 305 providing a signal to a lowfrequency receiver. Each fiber 713, 715 is characterized by a specificpattern or frequency, and each ONU 714, 716 sets its wavelengthdepending on the fiber 713, 715. The Piezo actuators 710, 712 may be ofthe type used in small speakers, operating on 3V approximately.

FIG. 8 depicts an embodiment for an active and passive splitter system.As shown in FIG. 8, regular passive splitters 804 a-804 n may follow anactive splitter 802. The active splitter 802 has N upstream detectors812 a-n each coupled to a WDM filter and keeps track of which detectors812 a-n receive optical input power. This is done by connections(arrows) from each detector to the micro-controller in block 813. Thisblock contains a microcontroller (uC) with A/D converters that canencode the detector current found at each of the detectors connected to813. The microcontroller can process the detector currents to determineif these are modulated, for instance with low frequency FSK signals, anddecode information encoded in the detector currents. The detectors alsoput out RF signals; the RF signals are preferably summed in atransmission line receiver structure and put out at an RF port 819.

The output of the RF port 819 can be provided to an RF amplifier 814that can have additional circuitry to detect tones (such as highfrequency FSK signals) or to detect the presence of OBI. Thus the activesplitter 802 may also detect tone or FSK signals sent upstream by theONUs e.g., ONUs 806 a-n, 808 a-n, 810 a-n, at low frequency or in the RFdomain. The circuit including a pre-amp, tone/OBI detect 814 can performthis function and OBI detection. The OBI detect function 814 can berealized by detecting noise in the signal to the pre-amplifier andflagging such an event to the microcontroller (uC) 813.

The FSK or tone detected signals may be provided to a microcontroller(uC) 813 with a tone of FSK signal generation capability. The tone orFSK signals can be sent to an LED 816 that provides light to thedownstream direction via a coupler 817 a, where the downstream signaldirection is coupled via 817 a to a 1×N splitter 803 that distributeslight over the N output ports. The signals from LED 816 can also be sentto the upstream transmitting laser (lsr) 815 that transmits informationin the upstream direction.

An EDFA 818 may be present to amplify downstream signals and the LEDlight from LED 816 can be injected in a coupler 817 b before the EDFA818. In embodiments, the ONU e.g., ONUs 806 a-n, 808 a-n, 810 a-n,detects OBI events that have been flagged to the uC 813 and signaledfrom the uC 813 to the LED 816 that transmitted this information to theONU. The microcontroller 813 may process OBI detect signals and output amodulation signal to a LED 816 (or laser) (e.g., via connection providedby the 1×N splitter 803) that injects a signal downstream with tone orFSK signaling for the ONUs. The output modulation signal may be injectedbefore or after an EDFA 818 amplifying the forward signal. Theembodiment shown in FIG. 8 may work with 1×4 passive splitters alreadyinstalled in the field, but will work with other splitters of varioustypes, that may be installed in the future. Disclosed is an opticalnetwork unit (ONU) for adjusting a wavelength operating with a splitterin an absence of optical beat interference (OBI). The ONU comprises aninput for receiving a downstream signal from a splitter opticallypowered without electrical power, the downstream signal identifying atleast one of a port over which the ONU is communicating with thesplitter or a wavelength at which another ONU is operating, and aprocessor for generating an ONU wavelength, wherein the wavelength isadjustable responsive to the downstream signal from the splitter. TheONU may use information in the downstream signal to configure itself fora connection to a port of the combiner, correlating information in thedownstream signal to the ONU's activity. The downstream signalidentifies a wavelength X for operation over connected port N, the ONUresponsive to the downstream signal for tuning to wavelength X. Thewavelength chosen is an indication of the port number of the splitter towhich the ONU is connected. For the ONU described, the ONU andcorresponding port may be used for system mapping.

The ONU can adjust its wavelength to avoid wavelengths taken by otherONUs. The ONU does not require a priori knowledge of combiner for ONUconfiguration. The ONU determines its configuration uni-directionalmanner. The ONU may further comprise a tone input for listening fortones or frequency-shift keying (FSK) signals in the downstream signalto determine at what wavelength it should operate. The ONU can decodesignaling informing about the port of an active 1×N splitter to which itis connected. The ONU may signal its current wavelength andidentification code upstream to the splitter. Responsive to identifyinga wavelength conflict with another ONU at the same port, the ONUwavelength is adjustable by the ONU. The downstream signal identifieswavelength labels for other ONUs connected to the splitter for selectinga non-conflicting wavelength. The downstream information identifiescurrently active upstream ports in use by the splitter.

In embodiments of the active/passive splitter system, the activesplitter keeps track of what ports receive upstream signals. Asillustrated in FIG. 8, in the downstream communication via the LED theactive splitter may provide a tag representing the active upstream portas a tone or FSK signal. In downstream communication the active splittermay embed information about upstream tones or FSK signals or OBI events.When multiple upstream ports are active, the active splitter can tag atransmission as multi-port or “invalid”. ONUs discard such “invalid”messages

In embodiments of the active/passive splitter system, ONUs filter outand select messages that are not “invalid”. ONUs self-learn what port ofthe active splitter they are on by correlating their own activity withactive port messages. ONUs filter messages for their own port to learnabout tone or FSK messages sent by other ONUs at the same port. ONUs canreceive signals for their own port when OBI events have been detectedspecific for that port

In embodiments of the active/passive splitter system, ONUs adjust theirwavelength according to the information received with a tag for theirport reporting OBI events or reporting what tone or FSK informationother ONUs connected to that port have sent. ONUs may send such tone orFSK signals to report their status, such as wavelength possiblyincluding serial number. The active splitter has a map of what ONUserial number is connected to what port. The active splitter may buildsuch a map and report it back to the headend to automatically build asystem map

In automatic full system mapping implementations, the large active 1×Nsplitter, when combined with smaller (non electrically powered) activesplitters with signaling may build a complete map of ONUs connected to1×N splitter and small splitter ports in the system. FIG. 8 illustratesa splitter 804 that may include such power harvesting with an automaticfull system mapping implementation. For example, the active 1×N splitterknows what ONUs are active and when, and the active 1×N splitter canmonitor chattering ONUs. In response, the headend can instruct such ONUsto shut down for maintenance

In embodiments that include cascading active splitters, such as thecascading splitters shown in FIG. 2, the cascaded active splitter maypreferably be operated at highest possible input power. Input powercoming from a downstream active splitter may vary depending on fiberloss. Noise Power Ratio (NPR) curves of cascaded active splitters may bepreferably aligned to overlap. Bidirectional communication can be usedto calibrate, and/or a calibration mode can be provided.

In embodiments for detecting and adjusting an input level in thepassive/active splitter system, an active splitter may measure currenton each input detector of the receiver. FIG. 8 is an example embodiment,depicting the pre-amp/tone/OBI detect circuit that may detect and adjustan input level in the passive/active splitter system, where reportingdownstream may be accomplished via the LED 816. In embodiments, theactive splitter may measure a level of a calibrated tone received fromeach downstream active splitter. The level of the calibrated tone, orcurrent, may be reported downstream so that a downstream active splittercan adjust output power and/or modulation index or gain.

In embodiments for entering a calibration mode in the passive/activesplitter system, a calibration mode of downstream active splitters maybe indicated by a downstream command. Downstream active splitters mayrandomly turn on with a low duty cycle, and an upstream active splittercan measures detector input power. An upstream active splitter canreport measurements to a downstream device, such as an index of portthat was active or “multi-port,” or a power received on that port. Adownstream device that is active may store the port index.

In embodiments for determining settings in a calibration mode in thepassive/active splitter system, when all ports have been assigned(passive ports time out if no power received), a processor ormicrocontroller in the active splitter may compute optimal output powersetting for each downstream active splitter, where the weakest link andport receive power limit can determine this setting. The active splittermay send instructions downstream for each port to downstream activesplitters (that now know their port numbers) to set these power level.In this manner, downstream devices can adjust gain accordingly to ensurenoise power ratio (NPR) curves overlap

In embodiments for verifying a calibration mode in the passive/activesplitter system, the active splitter may send instructions downstream toturn on ports, such as instructions for cycling through all ports and/orto verify power levels measured. If the verification fails, theprocedure may be repeated or time out and report upstream if there aretoo many failures. The instructions may be sent downstream for allactive splitters to switch to normal operation. The active splitter maymonitor port levels and report upstream as an element mapping system(EMS) to detect fiber breakage or other degradation of link. The EMS isa type of bidirectional communication system for monitoring and managingelements in the network, such as active splitters and ONUs.

In embodiments for the active/passive splitter system, ONU level ismonitored. In embodiments, an active splitter connected to ONU maymonitor optical power level per port. The levels may be reportedupstream to detect faults. If the ONU embeds tone or FSK labeling of ONUnumber, then faults can be related to ONU. Using the ONU labelingsignals, a full system map can be automatically built. In embodiments,active splitters can also send upstream tone or FSK information toidentify splitter

In embodiments described herein, the optical combiner provides upstreamand downstream RFoG capability and a completely transparent andreciprocal avenue for PON transmission. The optical combiner may enablecomplete transparency for PON deployments. For example, the opticalcombiner may enable OBI free and high capacity features by deployment incompatible HFC D3.1 capable FTTH networks. Likewise, the opticalcombiner may be incorporated in to GPON, 1G-EPON, XGPON1, 10G/1G-EPON,10G/10G-EPON. The compatibility with HFC and D3.1 enables the disclosedoptical combiner to be deployed alongside a current HFC network, and isD3.1 ready. The optical combiner may be deployed on a fiber node, onmultiple dwelling unit (MDU) and on single family home (SFU)deployments.

Embodiments for an RFoG combiner include preventing or eliminating OBIat the combiner as opposed to managing it at the extremities of thenetwork (such as using a CMTS scheduler at the headend side of thenetwork or wavelength specific ONUs at the subscriber end of thenetwork). Embodiments are described that enable elimination of OBI. Thedisclosed optical combiner may be used to eliminate OBI, enhancecapacity, and/or enable multiple services in RFoG, the cable version ofFTTH networks.

Disclosed are embodiments for an active receiver structure that combinesa large number of detectors without bandwidth penalty and provides abetter SNR than conventional RFoG. In embodiments, an opticalmultiplexer structure is designed around the active splitter such thatpassive PON network operation is not impeded. In embodiments, the activereceiver handles RFoG signals, not PON signals.

As described above, conventional implementations use multiple receiversthat are RF combined resulting in much higher cost, more powerdissipation and poorer noise performance. Optical Beat Interference(OBI) and the limited return link budget are problems in RFoG returnnetworks (seehttp://www.scte.org/documents/pdf/Standards/ANSI_SCTE_174_2010.pdf foran overview of RFoG networks). In such networks typically a starsplitter distributes light over 32 subscribers, the same splittercombines return light from the 32 subscribers at a penalty of 15 dB ofloss. The use of multiple receivers is not designed to handle activecombining of RF signals and passive PON splitting in one small unit.Also the optical combining of multiple sources at nominally the samewavelength can cause optical beat interference such that the informationcontent can be overwhelmed by noise.

Some embodiments for a photon harvester include techniques for photonharvesting signaling and optical combining that eliminate power in acombiner while maintaining an elimination or prevention of OBI. Inembodiments, the photon harvester is located in a passive combiner andharvests optical power from downstream light received at the combiner. Aportion of the light is detected by a photodiode and a charge producedin the photodiode is ingested by a capacitor. A downstream signal outputfrom the photon harvester driving a means to modulate an output signalmay inform an ONU to which port of the combiner it is connected and/orcause an ONU to changes its wavelength and/or cause the ONU to configureitself to the port to which it is connected.

In embodiments for the combiner described herein, the combiner is asingle SKU, non-active, and completely OBI eliminating passive combiner.

In embodiments for use with the combiner described herein, the ONU lacksa prior knowledge regarding the combiner and the configuration needed tocommunicate with the combiner.

In embodiments for the combiner described herein, the combinercommunicates settings to the ONU in a passive manner without usingelectrical power.

Some embodiments for the combiner described herein include a PZT drivercircuit that accepts charge discharged from a capacitor for travelingacross an active downstream channel. The PZT driver drives a Piezoelement that flexes a downstream fiber such that the optical loss of thefiber is modulated. Thus the intensity of downstream light is modulatedresulting in a signal to the ONU. The signal sent downstream from thePZT driver circuit is recognizable by the ONU and, in response to thesignal, the ONU determines whether to change its wavelength and/or thesignal causes the ONU to set its wavelength depending on a fibercharacterized by a pattern or frequency in a signal induced by the PZTdriver circuit.

Some embodiments for the combiner described herein include an LED drivercircuit that accepts charge discharged from a capacitor for travelingacross an active downstream channel. In embodiments, LEDs operate at lowduty cycles to inject forward signaling into a splitter with portinformation. The information is passed downstream to an ONU in adownstream signal, the downstream signal causing the ONU to determinewhether to change its wavelength and/or the signal causes the ONU to setits wavelength according to an assigned port.

In one or more examples, the functions described herein may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium and executed by a hardware-based processingunit. Computer-readable media may include computer-readable storagemedia, which corresponds to a tangible medium such as data storagemedia, or communication media including any medium that facilitatestransfer of a computer program from one place to another, e.g.,according to a communication protocol. In this manner, computer-readablemedia generally may correspond to (1) tangible computer-readable storagemedia which is non-transitory or (2) a communication medium such as asignal or carrier wave. Data storage media may be any available mediathat can be accessed by one or more computers or one or more processorsto retrieve instructions, code and/or data structures for implementationof the techniques described in this disclosure. A computer programproduct may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

We claim:
 1. A splitter/combiner unit for signaling to an opticalnetwork unit in an absence of optical beat interference (OBI), thesplitter/combiner unit comprising: a first input for receivingdownstream light; a second input for receiving upstream light from atleast one ONU; and at least one output for providing the downstreamlight in response to upstream light received from the at least one ONU,wherein the splitter/combiner unit is configured to signal the receiveddownstream light across an active downstream channel to the at least oneONU for causing an adjustment to the wavelength over which the ONUcommunicates with the splitter/combiner unit, wherein the ONU isresponsive to the signaling for adjusting said wavelength.
 2. Thesplitter/combiner unit of claim 1, further comprising: a photodiode fordetecting a portion of the downstream light; and a harvester unit foringesting electrical charge produced by photodiode for powering thesplitter's signaling to the optical network unit (ONU) without use ofadditional electrical power, wherein the harvester unit is discharged onto a circuit for signaling across an active downstream channel to theoptical network unit responsive to the signaling for adjusting awavelength of the optical network unit for communicating with thesplitter.
 3. The splitter/combiner of claim 2, wherein the signalingidentifies to the ONU a port of the splitter over which the signaling tothe optical network unit occurs.
 4. The splitter/combiner of claim 2,where in a wavelength of the optical network unit is adjustable by theoptical network unit in response to the signal received at the ONU. 5.The splitter/combiner of claim 2, wherein the harvester unit dischargeson to a piezo actuators (PZT) circuit or light emitting diode (LED)driver circuit for traveling across the downstream channel.
 6. Thesplitter/combiner of claim 5, wherein the PZT circuit drives a piezoelement that flexes a downstream fiber such that the optical loss of thefiber is modulated, the modulated optical loss of the fiber generates asignal recognizable to the ONU for determining whether to adjust itswavelength, and the generated signal causes the ONU to set itswavelength depending on the fiber characterized by a pattern orfrequency in the signal induced by the piezo actuators (PZT) drivercircuit.
 7. The splitter/combiner of claim 6, further comprising a lightemitting diode (LED) circuit that accepts charge discharged from theharvester unit for forwarding the signal across the active downstreamchannel, wherein the LED is configured for injecting forward signals into the splitter's input that identify port information for deliveringvia the port outputs to the connected ONUs, the LED configured foroperating at low duty cycles to inject forward signaling into a splitterwith the port information.
 8. The splitter/combiner of claim 2, furthercomprising a light emitting diode (LED) that turns on when sufficientpower has been collected by the harvester unit and forwards informationin a forward band as a tone/FSK (frequency shift keying) signal thatrepresents information detected by the photodiode.
 9. Thesplitter/combiner of claim 1, wherein the splitter/combiner is acompletely OBI eliminating passive combiner without an externalelectrical power connection.
 10. The splitter/combiner of claim 1,wherein the active splitter behaves passively with respect to signalingto the ONU without electrical power.
 11. The splitter/combiner of claim1, wherein the combiner includes active electrical components.
 12. Thesplitter/combiner of claim 1, wherein the active splitter may be locatedat an extremity of a network where no power is available.
 13. Thesplitter/combiner of claim 1, wherein the signaling from the splitterinstructs the ONU to select a particular wavelength depending on thesplitter's port involved in the signaling.
 14. The splitter/combiner ofclaim 1, further comprising a coupler and a reflecting device forre-injecting reverse light comprising a fraction of the ONU's light in aforward direction in to the coupler for distributing a fraction of theforward light of the ONUs to another one or more ONUs connected to thesplitter.
 15. The splitter/combiner of claim 1, wherein a wavelength ofthe another one or more ONUs connected to the splitter are adjustable bya respective ONU's response to signaling from the splitter/combineridentifying wavelengths that the another one or more ONUs aretransmitting on to prevent a wavelength conflict between ONUs.
 16. Thesplitter/combiner of claim 1, wherein at least one output is configuredfor splitting a signal propagated along a forward path direction into aplurality of forward path signals.
 17. The splitter/combiner of claim 1,wherein the second input is configured for receiving respective opticalsignals from each of the plurality of subscribers, combining the inputsfrom the plurality of subscriber to create a combined electrical signal,and converting the combined signal to an optical signal.
 18. Thesplitter/combiner of claim 1, further comprising a light emitting diode(LED) that produces a voltage with a tone/FSK (frequency shift keying)signal in response to receipt from an ONU transmitting in a reversedirection of a tone or FSK signal, the signal from the ONU includinginformation corresponding to a wavelength at which the ONU is operating.19. The splitter/combiner of claim 18, wherein the LED injects forwardsignals in to the splitter's input in response to upstream signalsreceived identifying at least one of an invalid combination ofwavelengths with the ONU operating wavelength, wherein the ONU isconfigured to reject a forward signal from the LED based on the invalididentification.
 20. The splitter/combiner of claim 1, further comprisinga light emitting diode (LED), wherein signaling to the ONU a port of thesplitter from which the signaling occurs comprises the LED forwardinginformation identifying wavelengths of any corresponding active ONUsconnected to the splitter to the ONU for identifying a non-conflictingwavelength.
 21. The splitter/combiner of claim 1, further comprising alight emitting diode (LED), wherein the LED used for forwardtransmission does not cause OBI with a forward signal.
 22. A system formanaging wavelength, the system comprising: a splitter/combiner unit forproviding downstream signals in response to upstream signals receivedfrom at least one optical network unit (ONU), wherein thesplitter/combiner unit signals the downstream signals across an activedownstream channel to the at least one ONU for causing an adjustment tothe wavelength over which the ONU communicates with thesplitter/combiner unit, wherein the ONU is responsive to the signalingfor adjusting said wavelength; at least one optical network unit foradjusting a wavelength operating with the splitter/combiner unit in anabsence of optical beat interference (OBI), the optical network unit forreceiving the downstream signal from the splitter/combiner unit, thedownstream signal identifying at least one of a port over which the ONUis communicating with the splitter or a wavelength at which another ONUis operating; and a processor for generating an ONU wavelength, whereinthe wavelength is adjustable responsive to the downstream signal fromthe splitter/combiner unit.